ANIMAL INTELLIGENCE. 31 



lous and adroit experimenters, the results ought to be verv vahi- 

 able. 



Surely every one must agree that no man now has a right to 

 advance theories about what is in animals' minds or to deny 

 previous theories unless he supports his thesis by systematic and 

 extended experiments. My own theories, soon to be pro- 

 claimed, will doubtless be opposed by many. I sincerely hope 

 they will, provided the denial is accompanied by actual experi- 

 mental work. In fact I shall be tempted again and again in the 

 course of this book to defend some theory, dubious enough to 

 my own mind, in the hope of thereby inducing some one to 

 oppose me and in opposing me to make the experiments I have 

 myself had no opportunity to make yet. Probably there will 

 be enough opposition if I confine myself to the theories I feel 

 sure of. 



Experiments with Dogs. 



The boxes used were as follows : 



A A was similar to A (O at front), except that the loop was 

 of stiff cord }i inch in diameter and was larger (3 ^ inches 

 diameter) ; also it was hung a foot from the floor and 8 inches 

 to the right of the door. The box itself w^as 41 x 20 x 23. 



BB was similar to B, the loop being the same as in AA, 

 and being hung a foot from the floor. The box was of the same 

 size and shape as AA. 



BBi was like BB, but the loop was hung 18 inches from the 

 floor. 



CC was similar to C (Button), but the button was 6 inches 

 long, and the box was 36^ x 22 x 23. 



II was similar to I, but the box was 30 x 20 x 25 inches; 

 the door (11 inches wide, 6 high) was in the left front corner, 

 and the lever was 6 inches long and entered the box at a point 

 2 inches to the right of the door and 4 inches above the floor. 



In M the same box as in II was used, but instead of a lever 

 projecting inside the box, a lever running outside parallel to 

 the plane of the front of the box and 18 inches long was used. 

 This lay close against the bars composing the front of the box, 

 and could be pawed down by sticking the paw out an inch or 



